WO2000052747A1

WO2000052747A1 - Method and system to uniformly etch substrates using an etching composition comprising a fluoride ion source and a hydrogen ion source

Info

Publication number: WO2000052747A1
Application number: PCT/US2000/005484
Authority: WO
Inventors: Kurt K. Christenson
Original assignee: Fsi International, Inc.
Priority date: 1999-03-03
Filing date: 2000-03-02
Publication date: 2000-09-08

Abstract

The present invention provides methods and a system for uniformly etching substrates. Specifically, the method and system of the present invention provide for the non-immersive contact of the substrate to be etched with an etching composition comprising a fluoride ion source and a hydrogen ion source. By utilizing an etching composition comprising such elements, not only is the etching of traditional substrate materials, i.e., silicon oxide, improved, but the etching of substrate materials traditionally difficult to etch satisfactorily, i.e., silicon nitride, is made possible.

Description

METHOD AND SYSTEM TO UNIFORMLY ETCH SUBSTRATES

USING AN ETCHING COMPOSITION COMPRISING A FLUORIDE ION SOURCE AND A HYDROGEN ION SOURCE

Field of the Invention

This invention relates to a non-immersive method and system for uniformly etching a substrate with an etching composition comprising a fluoride ion source and a hydrogen ion source. Furthermore, by identifying and optimizing several processing variables, the method and system of the present invention are able to enhance uniformity-related characteristics of substrates contacted by the etching composition.

Background of the Invention

The manufacture of microelectronic devices (integrated circuits, thin film heads, flat panel displays, other semiconductor devices and the like) involves numerous steps that are generally directed toward the formation of one or more layers or structures on a suitable substrate. According to common methodologies, operable layers and structures are often formed by first depositing various kinds of materials onto the substrate after which all or selected portions of such deposited materials may be removed via etching to create the layers and/or structures.

Etching quality is subject to stringent industry specifications. As one example, industry specifications may require that silicon oxide (SiO ) and/or silicon nitride (Si₃N₄) surfaces be etched to a uniformity of 2% or less. As the feature density of microelectronic devices becomes increasingly larger, etching uniformity specifications may become even more stringent, i.e., uniformity requirements of 1% or less may be required. Clearly, there is a need for improved etching techniques that provide better uniformity.

Etching involves contacting the material to be etched with a suitable etching composition, or "etchant", for a predetermined period of time. The quality of etching, and in particular the uniformity of the etched surface, depends upon the manner in which the material to be etched is contacted with the etchant, the nature of the etchant, and the nature of the material being etched. In terms of the manner by which the etchant is contacted with the material to be etched, etching techniques can be classified as immersive or non-immersive. Immersive etching, also known as "wet bench" etching, involves submerging the material in a suitable etchant. Non-immersive etching involves causing a liquid etchant to flowingly contact the material without submerging the etchant in the liquid. For example, the MERCURY^® spray processors commercially available from FSI International, Chaska, MN, non-immersively etch wafers by spraying etchant onto one or more wafers supported upon a rotating turntable.

Etchants that etch some materials satisfactorily do not etch others in a satisfactory manner. An excellent example of this difference is illustrated by the ease by which common etchants used to etch silicon oxide substrates in wet bench applications do not perform as well when used to etch silicon nitride in the same application. For example, solutions of hydrofluoric acid (FIF) in water and/or ethylene glycol can provide a uniformity on the order of 2% or slightly better of silicon oxide in wet bench etching applications, but provide 5% uniformity or worse when used to etch silicon nitride in the same wet bench applications. Such poor uniformity is not acceptable in most semiconductor device applications.

Thus, there is a need for an efficient method and system capable of producing etched substrates with a desired level of a predetermined uniformity- related characteristic. In particular, it would desirable for such a method and system to be capable of providing such a level of uniformity when applied to substrates comprising materials that are otherwise difficult to etch uniformly, e.g., silicon nitride.

Summary of the Invention

According to the present invention, the above objectives and other objectives apparent to those skilled in the art upon reading this disclosure are attained by the present invention which is drawn to a method and system for uniformly etching substrates. Specifically, the method and system of the present invention non-immersively contact the substrate to be etched with an etching composition comprising a fluoride ion source and a hydrogen ion source. By identifying and optimizing a number of preselected processing variables, the method and system of the present invention are capable of providing a high level of uniformity, e.g., < 1%, when used to etch a wide variety of materials, including both silicon oxide and silicon nitride.

Thus in one aspect, the present invention provides a method of uniformly etching at least a portion of a surface of at least one substrate with an etching composition. Specifically, the method comprises the steps of providing an etching composition comprising a fluoride ion source and a hydrogen ion source and subsequently causing the etching composition to non- immersively contact at least a portion of a surface of the substrate under conditions effective to uniformly etch at least a desired portion of the substrate surface.

In another aspect, the present invention provides a method comprising the step of determining the relationship that a processing variable of the method has on a uniformity-related characteristic of etched substrates produced by the method. A value for the processing variable is then preselected at which the etched substrate will meet a predetermined uniformity-related specification. The method then provides that the substrate is then contacted with the etching composition in accordance with the predetermined processing variable value so as to produce etched substrates that meet the predetermined uniformity- related specification.

In yet another aspect, the present invention provides a system for uniformly etching at least a portion of a surface of at least one substrate with an etching composition comprising a fluoride ion source and a hydrogen ion source comprising a chamber in which at least one substrate can be positioned for treatment with the etching composition comprising a fluoride ion source and a hydrogen ion source; a fluid supply comprising the etching composition; and a fluid supply line in fluid communication with the chamber through which the supply comprising the etching composition can be dispensed into the chamber in a manner such that the at least one substrate is non-immersively contacted with the etching composition. Preferably, the system further comprises an in-line heater operationally located in relation to the fluid supply line so that the temperature of the etching composition may be controlled. The system also preferably comprises at least one nozzle operationally coupled to the fluid supply line so that the fluid supply is dispensed from the fluid supply line into the chamber through said nozzle. It is further preferred that the chamber comprise a rotatable support structure capable of supporting one or more substrates.

As used herein, the term "uniformity" is meant to indicate the uniformity of an etch as determined in the following manner. The thickness of a film on a substrate is measured on a Rudolph Caliber 300 ellipsometer at 49 sites substantially evenly distributed across the substrate surface before and after each etch. The average removal, x, is calculated and is the average of the differences between the pre and post measurements of the 49 sites:

Average removal = x = Σ (pre-etch measurement - post-etch measurement) /49

The uniformity of the etch is defined as the standard deviation, σ, of the 49 removals. Uniformity may also be expressed as a percentage. Percent uniformity is defined as 100 times the standard deviation of the removals divided by the average removal.

% uniformity = (100 x σ) / x

The phrase "non-immersively contact", as used herein, means contact that does not result in a substrate being substantially totally submerged in etching composition.

Brief Description of the Figures

The above mentioned and other advantages of the present invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of the embodiments of the invention taken in conjunction with the accompanying drawing, wherein:

Figure 1 is a side schematic view of one representative system capable of treating a plurality of substrates with an etchant composition comprising a fluoride ion source and a hydrogen ion source in accordance with the present invention, wherein the system may typically comprise one to eight wafer cassettes and shows a central spray post for the delivery of etching composition;

Figure 2 is a top cross-sectional schematic view of a preferred embodiment of the system shown in Figure 1, wherein the cross-section is taken along line A- A, and wherein the system comprises two wafer cassettes and shows both a central spray post and a peripheral spray post for the delivery of etching composition;

Figure 3 is a top, cross-sectional schematic view of a preferred embodiment of the system shown in Figure 1, wherein the cross-section is taken along line A- A, and wherein the system comprises four wafer cassettes and shows both a central spray post and a peripheral spray post for the delivery of etching composition;

Figure 4 is a top, cross-sectional schematic view of a preferred embodiment of the system shown in Figure 1, wherein the cross-section is taken along line A-A, and wherein the system comprises one wafer cassette positioned centrally within the chamber and the etching composition is delivered from a peripheral spray post;

Figure 5 is a side schematic view of a preferred embodiment of the system shown in Figure 1, wherein the system does not comprise a wafer cassette, but rather a single wafer is positioned at a central position on the rotating support and the etching composition is delivered to the wafer from a central spray post.

Detailed Description of the Invention

The embodiments of the present invention described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the present invention.

The present invention provides methods and a system for uniformly etching substrates. Specifically, the method and system of the present invention provide for the non-immersive contact of the substrate to be etched with an etching composition comprising a fluoride ion source and a hydrogen ion source. By using an etching composition comprising such elements in a non-immersive process, not only is the etching of traditional substrate materials, i.e., silicon oxide, improved, but the etching of substrate materials traditionally difficult to etch satisfactorily, i.e., silicon nitride, is made possible. In fact, whereas the etching of silicon nitride by traditional methods produces etched substrates with unsatisfactory uniformity, the etching of silicon nitride utilizing the method of the present invention, produces substantially uniformly etched substrates.

While not wishing to be bound by any theory, it is believed that the etching of silicon nitride (Si₃N ) utilizing an etching composition in accordance with the present method consumes, neutralizes or otherwise reacts with byproducts of the etch reaction that might otherwise act to "poison" the etch. That is, the etching of silicon nitride by traditional methods, i.e., by contacting the silicon nitride substrate with aqueous hydrofluoric acid (HF), is believed to proceed according to the following reaction:

Si₃N₄ + 12 HF + 4H₂O → 3SiF₄ + 4NH₄UH

It is believed that the ammonium hydroxide produced by this etching reaction may act to at least partially neutralize the hydrofluoric acid etchant, thereby reducing the effectiveness of the etch. It is further believed that the hydrogen ion source that is included in the etching composition in accordance with the method of the present invention reacts with the formed ammonium hydroxide so that the ammonium hydroxide has a reduced tendency to react with and neutralize the hydrofluoric acid. Thus, the hydrofluoric acid remains available to etch the substrate, and a high quality etch is achieved. The hydrogen ion source of the etching composition may be any substance capable of providing a hydrogen ion to the etching composition separate and distinct from the fluoride ion source. It is preferred that the hydrogen ion source be a substantially non-etching acid so that the hydrogen ion source does not otherwise alter the characteristics of the etch, i.e., the etch rate, effectiveness of the etch on a variety of substrates, and the like. As used herein, the phrase "substantially non-etching acid" means an acid that, when placed in contact with a substrate, either does not etch the substrate at all, or etches the substrate only to a negligible degree, i.e., at an etch rate of from about 0 angstroms per minute to about 5 angstroms per minute. For example, suitable hydrogen ion sources include, but are not limited to, hydrochloric acid, sulfuric acid, nitric acid, acetic acid, combinations thereof and the like.

The etching composition in accordance with the method of the present invention further comprises a fluoride ion source. The fluoride ion source may be any source capable of providing a fluoride ion to the etching composition. Suitable fluoride ion source includes, but are not limited to, hydrofluoric acid, ammonium fluoride, buffered hydrofluoric acid, combinations thereof and the like.

Particular formulations of an etching composition in accordance with the method of the present invention can be determined with a view toward desired etch parameters, i.e., etch rate and etch uniformity. In general, enough of the fluoride ion source should be included so that the etch proceeds at a reasonable rate and a uniform etch is achieved. Enough of the hydrogen ion source should be included to enhance the quality of the etch. In the case of silicon nitride, enough of the hydrogen ion source is preferably included to consume, or otherwise ameliorate the action of, the by-products produced by the etch reaction. Of course, relative amounts of the hydrogen ion source to the fluoride ion source will depend on the particular combination of hydrogen ion source and fluoride ion source chosen. Bearing these considerations in mind, in preferred etching compositions wherein the hydrogen ion source comprises hydrochloric acid and the fluoride ion source comprises hydrofluoric acid, it is preferred that the hydrochloric acid to hydrofluoric acid weight ratio is in the range of from about 1 :20 to about 20: 1, more preferably, from about 1 :5 to about 5:1, most preferably, from about 2:3 to about 3:2.

In certain preferred embodiments, the etching composition in accordance with the method of the present invention may further comprise a solvent. Preferred solvents include water, organic solvents with ionization and solvation behavior similar to that of water, and combinations thereof. Exemplarly organic solvents suitable for use in the etching composition of the present invention include, but are not limited to, glycerol and ethylene glycol. The use of ethylene glycol as the solvent is particularly preferred inasmuch as ethylene glycol exhibits ionization and solvation behavior similar to that of water, but yet has a substantially higher boiling point. Thus, the use of ethylene glycol as the solvent provides an etching composition that may be used in applications wherein relatively high processing temperatures are desired.

If included, the solvent is preferably included in an amount that gives the resulting etching composition the desired etch characteristics, e.g., etch strength and etch rate, and flow characteristics, e.g., viscosity. The amount of the solvent required to provide the desired etch and flow characterisitics will depend on the particular solvent, hydrogen ion source and fluoride ion source selected, as well as on the intended manner of delivery of the etching composition, the desired temperature of the etching composition, and the like. For example, in those preferred embodiments wherein the etching composition comprises hydrochloric acid, hydrofluoric acid and ethylene glycol, and the etching composition is to be sprayed onto the substrate at a temperature of approximately 80°C, the etching composition preferably comprises from about 0.1 parts by weight (pbw) to about 15 pbw, more preferably, from about 1 pbw to about 5 pbw hydrofluoric acid, and from about 0.1 pbw to about 15 pbw, more preferably, from about 1 pbw to about 5 pbw hydrochloric acid per about 70 pbw to about 100 pbw ethylene glycol. Of course, inasmuch as the acids may be supplied as aqueous solutions, the resulting etching composition may comprise a corresponding amount of water.

Once the desired etching composition has been prepared, the etching composition is caused to non-immersively contact the surface of the substrate to be etched. In contrast to the present invention, many immersion techniques have limited utility in certain applications where it is desired to etch certain substances that are otherwise difficult to etch. This is believed to be due to the limitations of the traditional chemistry used therein or to the fluid dynamics of immersion techniques. For example, in wet bench etching applications, the etching composition is typically only infrequently and/or poorly refreshed at the etching surface, if refreshed at all. Thus, as etching proceeds in these applications, the etching composition may become less effective over time, resulting in reduced or inconsistent etch rates and unsatisfactory etch uniformity. In contrast by employing the etching composition of the method of the present invention and applying it in a non-immersive manner, many types of substrates may be etched to a better level of uniformity. More specifically, it is believed that the achievable uniformity is enhanced due to a combination of the etching performance of the etching composition, as well as by the fact that the non-immersive contact of the substrate with the etching composition results in the etching composition being substantially continually refreshed at a relatively high rate. As a result, the etched substrates produced in accordance with the method of the present invention have a level of uniformity not easily achieved in wet bench applications.

The etching composition in accordance with the method of the present invention may be applied to the substrate in one or more non-immersive manners. For example, as shown in Figure 5 discussed in more detail hereinbelow, the etching composition may be caused to flow across the surface of the substrate by, e.g., by dispensing the etching composition in a fluid stream from a source operably placed so that the etching composition contacts the substrate. As another option, the etching composition may be sprayed onto the substrate(s) to be etched using an appropriate spraying apparatus. One particularly preferred apparatus that may be used to spray substrates with the etching composition in accordance with the present invention is the centrifugal spray processor commercially available from FSI International, Chaska, Minnesota, under one or more of the trade designations MERCURY^®, SATURN^®, TITAN^®, or ZETA^®. In addition to providing a unique etching composition and causing the etching composition to non-immersively contact the substrate to be etched, the method and system of the present invention advantageously may, if desired, further provide for the determination of the relationship between a processing variable and at least on uniformity related characteristic, and selection of a value for the processing variable at which the etched substrate will meet a predetermined uniformity-related specification. By identifying such uniformity-related characteristics and determining the relationship between a processing variable and the characteristic, a processing variable value may be selected that can be implemented to achieve an etched substrate that will meet the predetermined uniformity-related specification. In this manner, the method and system of the present invention may beneficially be used to etch substrates that may be otherwise difficult to etch using traditional methods and/or etching compositions, e.g., silicon nitride. The method and system of the present invention may also be used to further improve the etch quality of other materials, such as silicon oxide, that are generally considered easier to etch.

For example, when using the etching composition in accordance with the invention in a centrifugal spray processor such as the MERCURY^® centrifugal spray processor, the number and placement of substrate cassettes, the rotational speed of the turntable on which the substrate(s) are supported, the temperature of the etching composition, the flow rate of the etching composition, and the location(s) from which the etching composition is delivered, may be studied and then particular values selected to provide substrates with a high level of etch uniformity. Each of these processing variables has an impact on the flow dynamics within the processor and thus, the contact of the substrates with the etching composition. By evaluating the impact of each of these processing variables on the quality of etch achieved on the substrate that is desirably etched, values for the variables can be preselected and utilized to provide etched substrates comprising a wide variety of materials with a desired level of uniformity. More specifically, the rotational speed of the turntable can be adjusted to control the length of time that the etching composition will stay in contact with the substrate surface, to control the motion or lack thereof of the etching composition across the substrate surface and to optimize the uniformity of contact between the etching composition and the substrate surface. Generally, rotational speeds of from about 20 rpm to about 750 φm have been found suitable to process most substrate materials.

The temperature of the etching composition may be adjusted to control the efficiency of the etch as well as to vary the viscosity of the etching composition, which will, in turn have an impact on the delivery of the etching composition and the length of contact between the etching composition and the substrate. For example, when the etching composition comprises a solvent that is tolerant of higher temperatures, temperatures in the range of from about 60°C to about 100°C have been found to be suitable in the processing of most substrate materials.

The flow rate of the etching composition and the location(s) from which the etching composition is delivered may be adjusted to control the length and uniformity of the contact between the etching composition and the substrates, which parameters will, in turn, have an impact on the etch rate and uniformity of the etch. In general, flow rates of from about 0.5 liters per minute to about 10 liters per minute from each of one or more spray posts located either centrally or peripherally to the rotating support have been found to be suitable in the processing of most substrate materials.

Finally, the number and placement of substrates and/or substrate cassettes has an impact on the flow dynamics within the processor and thus the length and uniformity of contact between the etching composition and the substrate(s). It has generally been found that a single substrate placed at a central location within the chamber, one substrate cassette placed at a central location within the chamber, two substrate cassettes placed substantially directly opposed to one another on the rotating support, or that four substrates placed at regular intervals around the periphery of the rotating support have been suitable to process most substrate materials.

The principles of the present invention can be incoφorated into a wide variety of methods and systems in which substrates are to be etched. Referring now to Figure 1, there is illustrated one example of a spray processing system 10 embodying the principles of the present invention. System 10, as illustrated, is adapted to uniformly etch at least a portion of a surface of one or more substrates 16 with an etching composition comprising a fluoride ion source and a hydrogen ion source. Generally, system 10 comprises chamber 118, fluid supply line 128, rotatable support 12, central spray post 124, and exhaust and drain line 112. System 10 further includes a peripheral spray post not shown in Figure 1 for the sake of simplicity. Chamber 118 is capable of housing one or more substrates 16 that are to be treated upon contact with etching composition 18.

Fluid supply line 128 serves to supply etching composition from an etching composition supply (not shown) into chamber 118. Fluid supply line 128 terminates at, and is operationally coupled to, central spray post 124 and/or a peripheral spray post (not shown in Figure 1) such that the etching composition 18 is dispensed into chamber 118 through one or both of these spray posts. Generally, central spray post 124 includes at least one complementary set, and preferably a plurality of complementary sets, of passages through which streams of etching composition supplied to central spray post 124 can be ejected in such a manner that at least one ejected stream of etching composition impacts at least one complementary ejected stream of an atomizing gas. The etching composition is atomized into a mist of droplets of etching composition 18 as a result.

Rotatable support 12 includes a top surface 110, a bottom surface 130, and a sidewall 14. Support posts 114 project upward from the top surface 110 of rotatable support 12 and are used to support one or more substrate cassettes 126 that hold a plurality of substrates 16 above rotatable support 12. Rotatable support 12 is itself supported on motor-driven shaft 120, which is capable of causing rotatable support 12 to rotate about an axis 122 central to motor-driven shaft 120.

During substrate etching, a desired flow rate of etching composition is dispensed from central spray post 124 (and/or a peripheral spray post that is not shown in Figure 1) in the form of atomized droplets of etching composition 18. In fact, the overall rate at which the etching composition is dispensed from central spray post 124 (and/or the peripheral spray post that is not shown in Figure 1) is one processing variable that may be optimized to produce an etched substrate with a high level of uniformity. Although the particular overall flow rate achievable from each spray post will depend on the viscosity of the etching composition utilized in the system of the present invention, the flow rate of etching composition delivered form each spray post will preferably be from about 0.5 liters per minute to about 10 liters per minute.

During the delivery of the etching composition, rotatable support 12 rotates to more evenly deposit the etching composition on the substrates 16. The rate of rotation of rotatable support is yet another processing variable that may have a value preselected so as to achieve a high level of etch uniformity. That is, depending on the nature and viscosity of the etching composition utilized in the system of the present invention, the rate of rotation of the rotatable support may be preselected to achieve a more uniform contact between the etching composition and the substrates. Preferably the rate of rotation of the rotatable support is preselected to be from about 20 φm to about 750 φm, more preferably from about 100 rpm to about 300 φm.

System 10 may further optionally include an in-line heater (not shown) operationally located in relation to fluid supply line 12 so as to be capable of heating the etching composition therein to a suitable temperature. Generally, the higher the etching temperature, the faster and more efficiently the etching process proceeds. Thus, the selection of the etching composition temperature is limited only to temperatures that are not so high as to cause the etching composition to degrade or boil. Thus, temperatures from about 60°C to about 100°C are preferred for etching compositions comprising ethylene glycol as a solvent. If such an in-line heater is included, it is preferably controlled by control methodology capable of controlling the temperature of the etching composition within desired specifications to further enhance uniformity of etching. Any control methodology capable of controlling temperature within specifications, i.e., ± 5°C, may be used. However, a preferred control methodology is described in co- pending U.S. Patent Application in the names of inventors Kurt Christenson et al., entitled "Method and Apparatus for Flowing Liquid Temperature Control", bearing attorney docket number 15676-217186 and filed on March 3, 1999, the full disclosure of which is incoφorated by reference herein.

Exhaust and drain line 112 is provided so that etching composition (and/or a purging gas, if employed) may be vented from chamber 118. Additionally, fluid supply line 128 and/or exhaust and drain line 112 may optionally comprise a flow regulating device (not shown) to regulate the flow of etching composition and exhaust, respectively.

The number and placement of substrate cassettes is yet another processing variable that may be varied in order to produce an etched substrate with a predetermined level of at least one uniformity-related characteristic. For example, a preferred embodiment of system 10, is illustrated in Figure 2. The embodiment of system 20 shown in Figure 2 is generally identical to system 10 illustrated in Figure 1, with the exception that two substrate cassettes 226 are arranged so as to be substantially directly opposed to one another on rotatable support 212. Figure 2 also shows central spray post 224 and peripheral spray post 230. Etching composition may be delivered from either one or both of central spray post 224 and/or peripheral spray post 230. If etching composition is to be delivered from both central spray post 224 and peripheral spray post 230, it is preferred that the volumetric flow rate of etching composition delivered from central spray post 224 to etching composition delivered from peripheral spray post 230 be from about 5:1 to about 1:5.

The embodiment of system 10 shown in Figure 2 is particularly advantageous because it can be used to etch silicon nitride substrates with a level of uniformity of from about 0.5% to about 1% by optimizing the parameters discussed above. Specifically, this level of uniformity has been achieved when the second etching composition, described in the Example, hereinbelow, is delivered from both central spray post 224 and peripheral spray post 230 at an overall flow rate of about 6 liters per minute and at a temperature of about 80°C. The etching composition so delivered is then caused to contact a plurality of substrates as supported on substrate supports 226 while rotatable support 212 rotates at a rate of about 120 φm.

An additional preferred embodiment of system 10 is illustrated in Figure 3 to further illustrate the manner in which the number and placement of substrate cassettes may be varied to achieve a high level of etch uniformity. The embodiment of system 30 shown in Figure 3 is generally identical to system 10 illustrated in Figure 1, with the exception that four substrate cassettes 326 are arranged at substantially regular intervals around the periphery of rotating support 312. The embodiment of system 10 shown in Figure 3 is particularly advantageous because it can be used to etch silicon nitride substrates with a level of uniformity of from about 0.5% to about 1% by optimizing the parameters discussed above. Specifically, this level of uniformity has been achieved when the etching composition is delivered from both central spray post 324 and peripheral spray post 330 at an overall flow rate from each spray post of about 6 liters per minute and at a temperature of about 80°C. The etching composition so delivered is then caused to contact a plurality of substrates as supported on substrate supports 326 while rotatable support 312 rotates at a rate of about 120 φm.

An additional preferred embodiment of system 10 is illustrated in Figure 4 to further illustrate the manner in which the number and placement of substrate cassettes may be varied to achieve a high level of etch uniformity. The embodiment of system 40 shown in Figure 4 is generally identical to system 10 illustrated in Figure 1, with the exception that one substrate cassette 426 is placed at a central position on the rotating support 412. The embodiment of system 10 shown in Figure 4 is particularly advantageous because it can be used to etch silicon nitride substrates with a level of uniformity of from about 0.5% to about 3% by optimizing the parameters discussed above. Specifically, this level of uniformity has been achieved when the etching composition is delivered from peripheral spray post 430 at an overall flow rate of about 6 liters per minute and at a temperature of about 80°C. The etching composition so delivered is then caused to contact a plurality of substrates as supported on substrate supports 426 while rotatable support 412 rotates at a rate of about 120 rpm.

Yet another preferred embodiment of system 10 is illustrated in Figure 5 to further illustrate the manner in which the number and placement of substrate cassettes may be varied to achieve a high level of etch uniformity. The embodiment of system 50 shown in Figure 5 is generally identical to system 10 illustrated in Figure 1, with the exception that system 50 illustrates a preferred embodiment wherein a single substrate 516 is placed within the chamber and is supported on rotatable support 512. The embodiment of system 10 shown in Figure 5 is particularly advantageous because it can be used to etch silicon nitride substrates with a level of uniformity of from about 0.5% to about 1%, preferably less than 0.5%, by optimizing the parameters discussed above. Specifically, this level of uniformity can be achieved when the etching composition is delivered from the central spray post 524 in a fluid stream at an overall flow rate of about 1 liter per minute and at a temperature of about 80°C. The etching composition so delivered is then caused to contact a substrate 516 while rotatable support 512 rotates at a rate of about 500 φm.

The present invention will be described below with reference to the following representative examples.

Example

200 mm silicon wafers with Si₃N₄ and SiO (nitride and oxide) films were etched in a MERCURY^® MP centrifugal spray acid processor (FSI International, Chaska, MN). In each process run, four nitride wafers were etched in positions 1, 13, 24 and 25 in a Fluoroware A192-81m process cassette (Fluoroware Inc., 102 Jonathan Ave. N., Chaska, MN 55318). A single oxide wafer was processed in slot 15 with balance wafers filling the rest of the cassette. An additional process cassette filled with balance wafers was placed at a position substantially directly opposed to the cassette comprising the test wafers on the rotating turntable. Most of the webbing had been manually cut away from the cassettes to improve fluid flow.

The control etching composition was prepared comprising a 96:4 vokvol blend of pure ethylene glycol (EG) and 49 wt% HF in water. The first sample etching composition was prepared comprising a 95.3:4:0.7 vol:vol:vol blend of pure EG, 49 wt% HF in water and 37 wt% HC1 in water. A second sample etching composition was prepared comprising a 92:4:4 vol:vol:vol blend of pure EG, 49 wt% HF in water and 37 wt% HC1 in water.

The etching compositions were pumped to the MERCURY® process chamber from a chemical recirculation unit and sprayed on the wafers from the peripheral spray post at a flow rate of 6 liters/min. The MERCURY® and recirculation unit plumbing were modified with high capacity tubing, valves, spray post and filter to support the 6 liter/min flow. Additionally, the fluid supply line was bifurcated so as to be capable of directing a flow of etching compostion to the peripheral spray post. After flowing over the wafers, the etching compositions collected at the bottom of the process chamber and flowed back to the storage tank in the recirculation system via a dedicated drain connection.

The temperature of the etching compositions in the storage tank of the recirculation unit was maintained near 80° C by a heat exchanger driven with hot DI water. The temperature of the etching compositions dispensed on the wafers was tightly controlled near 82°C by an in-line, infra-red chemical heater utilizing a feed forward temperature control algorithm (described in co-pending

U.S. Patent Application in the names of inventors Kurt Christenson et al., entitled

"Method and Apparatus for Flowing Liquid Temperature Control", bearing attorney docket number 15676-217186 and filed on March 3, 1999) yielding an on-wafer temperature near 80°C.

The full process sequence was as follows:

• A 360 second pre-heat of the wafers with hot DI water (95 °C) delivered from the central spray post while the rotating support was caused to rotate at a rate of about 200 φm and a simultaneous 360 second pre-heat of the fluid supply line with hot etching composition (82°C); • A 35 second high speed spin of the wafers at 500 rpm to remove the hot DI water;

• A 25 second period to decelerate the rotatable support to 120 φm;

• A 260 second etch in etching composition while the rotating turntable was caused to rotate at a rate of 120 rpm in both clockwise and counter-clockwise directions as follows:

• 120 rpm clockwise for 44 seconds while etching composition (at 82°C) was delivered from the peripheral spray post at a rate of about 6 liters per minute, followed by a 10 second intermediate reversal step with no delivery of etching composition;

• 120 φm counter-clockwise for 44 seconds while etching composition (at 82°C) was delivered from the peripheral spray post at a rate of about 6 liters per minute, followed by a 10 second intermediate reversal step with no delivery of etching composition;

• 120 φm clockwise for 44 seconds while etching composition (at 82°C) was delivered from the peripheral spray post at a rate of about 6 liters per minute, followed by a 10 second intermediate reversal step;

• 120 φm clockwise for 44 seconds while etching composition (at 82°C) was delivered from the peripheral spray post at a rate of about 6 liters per minute.

• Standard purging sequence as follows:

• The rotating turntable was caused to reverse while no etching composition was delivered to the wafers for a period of 10 seconds;

• Ambient temperature nitrogen was caused to flow through the fluid supply line while the rotating turntable was caused to rotate counter clockwise at a rate of 120 φm for 44 seconds; • The etching composition within the fluid supply line (approximately 60 cc etching composition) was forced out of the fluid supply line and onto the wafers by a flow of ambient temperature nitrogen for 10 seconds;

• Ambient temperature nitrogen was caused to flow through the fluid supply line while the rotating turntable was caused to reverse to a clockwise rotation for 10 seconds;

• A rinse sequence that initially quenches the etch reaction and then thoroughly cleans the wafers and the chamber was used. Specifically, the rinse sequence proceeded with an initial 65 second rinse sequence with cold distilled water at approximately 20°C, followed by six (6) rinse sequences utilizing cold and hot water (95°C) simultaneously. The rotational speed of the wafers was varied in accordance with the standard rinse cycle used in the MERCURY® centrifugal spray processor, except that the rinse cycle was modified to allow rinsing of both the central spray post and the peripheral spray post inasmuch as the peripheral spray post was used to dispense etching composition in the present example. Rotational speeds cycled between 500, 60, and 20 φm, through the initial 65 second cold rinse sequence. Cold distilled (DI) water was dispensed continuously from a dedictaed rinse source from the center spray post to rinse the wafers and through the fan jets provided on the rotatable support of the MERCURY® spray processor to rinse the chamber. The fluid supply line was alternately rinsed with cold water and purges with ambient nitrogen during this sequence. The principles of this kind of rinsing sequence, in which the rotational speed of the rotatable support is varies is described in K. Christenson, "Rinsing: A critical process in contamination removal", Semiconductor Fabtech., 6^th edition, IGC publishing, London (1997) pg 333, the full disclosure of which is incorporated by reference herein.

• Standard dry sequence - A 5 minute purge of all liquid lines with ambient dry nitrogen while the turntable was caused to rotate clockwise at 500 φm.

The process results for the standard and sample etching compositions were as follows:

Other embodiments of this invention will be apparent to those skilled in the art upon consideration of this specification or from practice of the invention disclosed herein. Various omissions, modifications, and changes to the principles and embodiments described herein may be made by one skilled in the art without departing from the true scope and spirit of the invention which is indicated by the following claims.

Claims

What is claimed is:

1. A method of uniformly etching at least a portion of a surface of at least one substrate with an etching composition comprising the steps of:

(a) providing an etching composition comprising a fluoride ion source and a hydrogen ion source; and

(b) causing the etching composition to non-immersively contact at least a portion of a surface of the substrate under conditions effective to uniformly etch at least a desired portion of the substrate surface.

2. The method of claim 1, wherein the fluoride ion source is selected from hydrofluoric acid, ammonium fluoride, buffered hydrofluoric acid, or combinations thereof.

3. The method of claim 2, wherein the fluoride ion source comprises hydrofluoric acid.

4. The method of claim 1, wherein the hydrogen ion source comprises a substantially non-etching acid.

5. The method of claim 4, wherein the hydrogen ion source is selected from hydrochloric acid, nitric acid, sulfuric acid, acetic acid or combinations thereof.

6. The method of claim 5, wherein the hydrogen ion source comprises hydrochloric acid.

7. The method of claim 1, wherein the etching composition comprises a weight ratio of hydrochloric acid to hydrofluoric acid of from about 1 :5 to about 5:1.

8. The method of claim 1, wherein the etching composition further comprises a solvent selected from the group consisting of water, glycerol, ethylene glycol or combinations thereof.

9. The method of claim 8, wherein the etching composition is prepared with a solvent comprising ethylene glycol.

10. The method of claim 8, wherein the etching composition comprises from about 0.1 pbw to about 15 pbw hydrofluoric acid, and from about 0.1 pbw to about 15 pbw hydrochloric acid per about 70 pbw to about 100 pbw ethylene glycol.

11. The method of 1, wherein the etching composition is caused to non- immersively contact at least a portion of a surface of a substrate comprising a semiconductor wafer.

12. The method of claim 11, wherein the etching composition is caused to non-immersively contact a semiconductor wafer comprising silicon nitride.

13. The method of claim 12, wherein the step of causing the etching composition to non-immersively contact the semiconductor wafer causes at least a portion of the surface of the semiconductor to have a percent uniformity of from about 0.5% to about 1%.

14. The method of claim 11, wherein the etching composition is caused to non-immersively contact a semiconductor wafer comprising silicon oxide.

15. The method of claim 1, wherein the step of causing the etching composition to non-immersively contact at least a portion of a surface of a substrate comprises contacting the substrate with the etching composition while the substrate is supported on a rotating support.

16. The method of claim 15, wherein the step of non-immersively contacting the substrate comprises causing at least one fluid stream comprising the etching composition to flow onto the substrate.

17. The method of claim 16, wherein the at least one fluid stream is caused to flow at a flow rate of from about 0.5 liters per minute to about 10 liters per minute.

18. The method of claim 15, wherein the step of non-immersively contacting the substrate comprises spraying the etching composition onto the substrate.

19. The method of claim 18, wherein the step of spraying the etching composition further comprises causing the etching composition to be atomized.

20. The method of claim 18, wherein the step of non-immersively contacting the substrate comprises positioning the substrate within a chamber comprising a central spray post and spraying the etching composition from the central spray post.

21. The method of claim 18, wherein the step of non-immersively contacting the substrate comprises positioning the substrate within a chamber comprising a peripheral spray post and spraying the etching composition from the peripheral spray post.

22. The method of claim 18, wherein the step of non-immersively contacting the substrate comprises positioning the substrate within a chamber comprising a central spray post and a peripheral spray post and spraying the etching composition from the central spray post and the peripheral spray post.

23. The method of claim 22, wherein the volumetric flow rate of the volume of etching composition sprayed from the central spray post to the volume of etching composition sprayed from the peripheral spray post is from about 5 : 1 to about

5: 1.

24. A method of uniformly etching at least a portion of a surface of at least one substrate with an etching composition comprising a fluoride ion source, a hydrogen ion source and a solvent, wherein the method comprises the steps of:

(a) determining the relationship between a processing variable of the method and at least one uniformity-related characteristic of the at least one etched substrate produced by the method;

(b) preselecting a value for the processing variable at which the etched substrate will meet a predetermined uniformity-related specification; and

(c) contacting the substrate with the etching composition comprising a fluoride ion source, a hydrogen ion source and a solvent, in accordance with at least the predetermined processing variable value so as to produce at least one etched substrate with the predetermined level of the uniformity-related characteristic.

25. The method of claim 24, wherein the processing variable is the flow rate of the etching composition and the processing variable value is preselected to be between from about 0.5 liters per minute to about 10 liters per minute.

26. The method of claim 24, wherein the processing variable is the temperature of the etching composition and the processing variable value is preselected to be between from about 60°C to about 100°C.

27. The method of claim 24, wherein the processing variable is the rotational speed of a support upon which the substrate is supported and the processing variable value is preselected to be a rotational speed of from about 20 φm to about 750 φm.

28. The method of claim 24, wherein the processing variable is the placement of the substrate relative to the source of the etching composition and the processing variable is preselected to comprise placing the etching composition source at a central position relative to the substrate.

29. The method of claim 24, wherein the processing variable is the placement of the substrate relative to the source of the etching composition and the processing variable is preselected to comprise placing the etching composition source at a peripheral position relative to the substrate.

30. The method of claim 24, wherein the processing variable is the placement of the substrate relative to the source of the etching composition and the processing variable is preselected to comprise placing a first etching composition source at a central position relative to the substrate and placing a second etching composition source at a peripheral position relative to the substrate.

31. The method of claim 24, wherein the processing variable is the number and relative placement of at least one substrate cassette on a rotating support and the processing variable is preselected to comprise two substrate cassettes placed so as to be substantially directly opposed to one another.

32. The method of claim 24, wherein the processing variable is the number and relative placement of at least one substrate cassette on a rotating support and the processing variable is preselected to comprise four substrate cassettes placed at substantially regular intervals around the periphery of the rotating support.

33. The method of claim 24, wherein the uniformity-related characteristic is the percent uniformity in the substrate surface and the predetermined level of percent uniformity is from about 0.5% to about 1%.

34. A system for uniformly etching at least a portion of a surface of at least one substrate with an etching composition comprising a fluoride ion source and a hydrogen ion source comprising:

(a) a chamber in which at least one substrate can be positioned for treatment with the etching composition comprising a fluoride ion source and a hydrogen ion source;

(b) a fluid supply comprising the etching composition; and

(c) a fluid supply line in fluid communication with the chamber through which the supply comprising the etching composition can be dispensed into the chamber in a manner such that the at least one substrate is non-immersively contacted with the etching composition.

35. The system of claim 34, further comprising an in-line heater operationally located in relation to the fluid supply line so that etching composition present within the fluid supply line is capable of being heated.

36. The system of claim 34, wherein the chamber comprises a rotatable support structure capable of supporting a plurality of substrates.

37. The system of claim 34, wherein the chamber comprises a recirculation pathway through which etching composition is recirculated and returned to the chamber.

38. The system of claim 34, further comprising at least one nozzle operationally coupled to the fluid supply line so that the fluid supply is dispensed from the fluid supply line into the chamber through said nozzle.

39. The system of claim 38, wherein the at least one nozzle is an atomizing spray post.

40. The system of claim 34, wherein the fluoride ion source is selected from hydrofluoric acid, ammonium fluoride, buffered hydrofluoric acid, or combinations thereof.

41. The system of claim 40, wherein the fluoride ion source comprises hydrofluoric acid.

42. The system of claim 34, wherein the hydrogen ion source comprises a substantially non-etching acid.

43. The system of claim 42, wherein the hydrogen ion source is selected from hydrochloric acid, nitric acid, sulfuric acid, acetic acid or combinations thereof.

44. The system of claim 43, wherein the hydrogen ion source comprises hydrochloric acid.

45. The system of claim 34, wherein the etching composition comprises a weight ratio of hydrochloric acid to hydrofluoric acid of from about 1 :5 to about

5: 1.

46. The system of claim 34, wherein the etching composition further comprises a solvent selected from water, glycerol, ethylene glycol or combinations thereof.

47. The system of claim 46, wherein the solvent comprises ethylene glycol.

48. The system of claim 46, wherein the etching composition comprises from about 0.1 pbw to about 15 pbw hydrofluoric acid, and from about 0.1 pbw to about 15 pbw hydrochloric acid per about 70 pbw to about 100 pbw ethylene glycol